The Lactase Activity of the Intestinal Mucosa of the Dog and Some Characteristics of Intestinal Lactase

The early work on intestinal lactase has been reviewed by Plimmer (1906) and Oppenheimer (1925). No uniformity of opinion was reached regarding the presence and dist,ribution of this enzyme in the intestinal mucosa or in intestinal juice. Without attempting to review these investigations again, it suffices to state that some authors found lactase in the small intestine of young animals. Others reported its presence in the intestine of adult animals as well. It is well known that animals do not utilize lactose readily when it is administered parenterally. When this sugar is given by mouth, however, it is absorbed and utilized. Unless the quantity fed is large, it is not excreted in the urine to any extent. Thus, all evidence points to the probability that lactose given per OS is normally hydrolyzed before it is absorbed (Corley, 1927). Heretofore, attempts to account for lactose absorption in terms of the observed lactase activity have not been successful. Rijhman and Nagano (1903) in their extensive study of sugar absorption in dogs found no lactase activity in intestinal juice and only slight activity in the mucosa. In the Thiry loops of their dogs the observed lactase activity was totally inadequate for the hydrolysis of the lactose absorbed from the loops. They concluded that this sugar was not hydrolyzed prior to its absorption as were sucrose and maltose. Cajori (1933) found that lactose was absorbed from intestinal loops of dogs much more rapidly than could have been predicted from the enzyme activity of the intestinal juice. The analytical methods available to the early investigators were